Embodiments relate to a semiconductor device and a method for forming the same, and more particularly to a semiconductor device including a buried bit line.
As highly integrated semiconductor devices have developed, cell structure (or cell layout) is changing from 8F2 and 6F2 structures to a 4F2 structure. In order to reduce the size of a unit cell, various methods for forming constituent elements (such as transistors, word lines, capacitors, and the like) have been developed by research institutions and companies. For example, a semiconductor device in which a source and a drain are vertically arranged to implement the 4F2 cell structure, and thereby inducing a vertical channel, has been proposed.
A semiconductor device having a vertical channel includes a gate electrode adjacent to an active pillar, which extends vertically from a main surface of a substrate. A semiconductor device having a vertical channel also includes sources and drains at portions of the active pillar that are over and under the gate electrode, respectively. As a result, a channel is vertically formed in a portion of the active pillar beneath the gate electrode. Since a channel is formed vertically, the length of the channel of the resultant semiconductor device may not be as significantly affected by a reduction in the size of a unit cell region of the semiconductor device.
A semiconductor device having a vertical channel may further include a buried bit line (BBL) structure in which a bit line is buried in a region of the substrate below the active pillar.
In the 4F2 structure, a buried bit line has a line shape and is formed of metal silicide. However, portions of the silicide line may aggregate so that the line has thinner portions, thereby increasing electrical resistance of the buried bit line.
In addition, during a plasma doping process to form a junction of the buried bit line, a bending or a leaning of an active region may occur due to plasma residue.
In a 6F2 structure, a process for etching the active region is carried out to define a buried bit line. Due to the etched active region, a contact region between a word line and an active region and/or a storage node contact (SNC) region may be reduced in size. As a result, control capability of word lines and an Iop are unavoidably reduced.